fox in the henhouse

Fox in the henhouse is the term used for a predator that is loose among the prey, typically a smaller type of wild animal. Literally speaking, a fox in the henhouse is extremely dangerous to the hens and chickens because the fox will more than likely kill many of these animals, or injure them at the very least. When use figuratively, this saying means virtually the same thing; that something dangerous is among what it is aiming for.